The construction of large dams such as the Alborz Reservoir Dam in spite of water supply in drinking and agricultural sectors is undoubtedly associated with large changes in natural ecosystems. Knowing and awareness of these changes is essential in order to plan and manage sustainable areas affected by the dam. simultaneous use of remote sensing and geographic information technology is one of the common methods for monitoring changes in the region. In this regard, the purpose of this study is to investigate the relationship between land cover / land use changes by constructing and dewatering of Alborz Dam using remote sensing and geographic information systems. To this end, two Landsat satellite images were used during the 22-year period (1994 and 2016) by applying radiometric and atmospheric correction as illustrating the changes in land cover / land use of the region before and after constructing. Then, , land cover/land use maps were produced by using the supervised classification method of the support vector machine and the accuracy of the classifications were evaluated and Analysis of time-varyings land cover / land use was also performed by producing of change detection map.In addition to, LQ index was used to study the spatial variations of different land cover / land use classes. According to the results, over two decades, the area of ​​forest cover increased by 22.7 hectares, the area of ​​agriculture and pasture, as well as construction areas decreased by 735.66 hectares and 17.82 hectares respectively and the area of water which has submerged the above classes, was 530.37 hectars.  Investigating the changes in the spatial pattern of land cover / land use showed that the most changes in the upstream side (dam reservoir) with LQ equal to 1.68, belongs to the water, which clearly indicates the effect of Alborz dam construction and dewatering on ​​land cover / land use changes at upstream side of the dam.